A common problem with telecommunications satellites is that of strong interference signals at certain frequencies, occupying one or more communications channels. This may arise for example by another operator leaving equipment on and unsupervised, or with antennae pointing in the wrong direction. This interfering signal may automatically be amplified by the satellite, and may render communications channels unusable. It may even allow unauthorised use of the broadcast function of the satellite by an unauthorised user.
WO 2006/043115 discloses a cost-effective analog mechanism that enables flexibility in the routing of channels between uplink and downlink beams, wherein all uplink channels from a variety of microwave bands are converted to a first IF, and agile filters are employed to filter and translate selected channels to a second IF, in order to group the selected channels together for transmission on a downlink beam.
Agile filters are known, and are for example described in U.S. Pat. No. 4,262,361, and WO 2006/085116, which provide a variable bandpass or bandstop function, with a mechanism for adjusting the position of bandpass edges, both in terms of centre frequency and in terms of width of the band. Such mechanism comprises a series of mixers for receiving the input signal and variable frequency local oscillator signals, for adjusting the position of the input signal by desired amounts in relation to filter edges.